include/asm-x86/timer.h

   1 #ifndef ASM_X86__TIMER_H
   2 #define ASM_X86__TIMER_H
   3 #include <linux/init.h>
   4 #include <linux/pm.h>
   5 #include <linux/percpu.h>
   6
   7 #define TICK_SIZE (tick_nsec / 1000)
   8
   9 unsigned long long native_sched_clock(void);
  10 unsigned long native_calibrate_tsc(void);
  11
  12 #ifdef CONFIG_X86_32
  13 extern int timer_ack;
  14 extern int recalibrate_cpu_khz(void);
  15 #endif /* CONFIG_X86_32 */
  16
  17 extern int no_timer_check;
  18
  19 #ifndef CONFIG_PARAVIRT
  20 #define calibrate_tsc() native_calibrate_tsc()
  21 #endif
  22
  23 /* Accelerators for sched_clock()
  24  * convert from cycles(64bits) => nanoseconds (64bits)
  25  *  basic equation:
  26  *              ns = cycles / (freq / ns_per_sec)
  27  *              ns = cycles * (ns_per_sec / freq)
  28  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  29  *              ns = cycles * (10^6 / cpu_khz)
  30  *
  31  *      Then we use scaling math (suggested by george@mvista.com) to get:
  32  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  33  *              ns = cycles * cyc2ns_scale / SC
  34  *
  35  *      And since SC is a constant power of two, we can convert the div
  36  *  into a shift.
  37  *
  38  *  We can use khz divisor instead of mhz to keep a better precision, since
  39  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  40  *  (mathieu.desnoyers@polymtl.ca)
  41  *
  42  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  43  */
  44
  45 DECLARE_PER_CPU(unsigned long, cyc2ns);
  46
  47 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  48
  49 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
  50 {
  51         return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;
  52 }
  53
  54 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  55 {
  56         unsigned long long ns;
  57         unsigned long flags;
  58
  59         local_irq_save(flags);
  60         ns = __cycles_2_ns(cyc);
  61         local_irq_restore(flags);
  62
  63         return ns;
  64 }
  65
  66 #endif /* ASM_X86__TIMER_H */